The present invention relates generally to a method and a structure for forming semiconductor substrates, and particularly relates to improvement in ceramic manufacturing process and structure for the production of ceramic packages using at least one thermally depolymerizable surface layer. More particularly, this invention relates to ceramic green laminate processing and structure using at least one protective overlay that adheres to at least a portion of the green ceramic surface to provide reduction/elimination of defects caused during processing, such as, handling and sizing/dicing operations.
Semiconductor substrates and devices are becoming smaller and more dense with the evolution of new technologies. However, increase in circuit density produce a corresponding increase in overall manufacturing problems. These manufacturing problems must however be kept to a minimum in order for the semiconductor manufacturer to remain competitive. The semiconductor manufacturers are therefore constantly being challenged to improve the quality of their products by identifying and eliminating defects which produce defective parts or components. Whereas significant improvements are being made to eliminate systematic defects by reducing process variability, process improvements alone are not sufficient to eliminate all the random defects which effect both yield and reliability. Historically, screening techniques have been employed to improve product failure rates to acceptable levels by culling out many of these random defects.
In their desire to improve their products, the semiconductor manufacturers are constantly finding new ways and new techniques to improve or provide new products. Semiconductor substrates or ceramic chip carriers generally are made with a planar surface having a flat chip site for mounting the semiconductor device. The substrates are often referred to as modules which can be made from a single ceramic layer or green sheet forming a single layer ceramic module or a plurality of ceramic layers could be used to form a multi-layer ceramic (MLC) module.
While the remaining discussion will be directed to MLC modules, it should be understood that the teachings of the present invention can be equally applicable to single layer modules.
MLC modules are normally used in the electronic industry to package high performance integrated circuits or chips (hereafter just chips). These high performance chips have a large number of external inputs/outputs (I/Os), such as pads or solder balls, to name a few, and these chips have a very high power dissipation requirement. In order to accommodate such high performance chips, the MLC module also has to provide a high number of external I/Os, such as pads, pins, solder balls, to name a few, and also be able to handle the very high power dissipation both from the module as well as the chip.
Standard process for ceramic substrate production involves green sheet casting of ceramic slurry comprising ceramic filler, organic binder, solvent vehicle and plasticizer dispersion, blanking, via punch, circuit personalization or screening of conductive paste through a screen mask, singulation/sizing, inspect/collate/register, stack and lamination, binder burn-off and sintering operations. In the handling of green laminates especially sizing and dicing operations, flying ceramic debris generally falls on the surface layer which gets embedded in the ceramic during subsequent processing, such as, the sintering process. Such defects in the ceramic substrates are undesirable and thus significant number of sintered substrates have to be reworked or discarded causing additional expenses and/or product yield losses.
The present invention, however, solves this problem by the use of a thermally depolymerizable/decomposable surface film or layer that protects the green ceramic surface during lamination, and also serves as a sacrificial protective layer against any flying ceramic debris during handling and sizing/dicing operations. However, the protective layer is preferably made from a material that decomposes and burns off during the sintering cycle.
The present invention is a novel method and structure for providing at least one sacrificial protective polymer adhesive layer over a green sheet laminate in order to minimize and/or eliminate processing defects. The surface protective film preferably comprises of at least one thermally depolymerizable polymer which cleanly burns off during the sintering cycle.
Therefore, it is a purpose of the present invention to provide an improved method for semiconductor substrate production without causing damage or defects to the ceramic body or causing paste pull-outs.
Another purpose of the present invention is to provide a thermally decomposable surface film, which film avoids any damage to the ceramic body and/or causes any paste pull-outs.
Yet another purpose of this invention is to provide a novel thermally depolymerizable/decomposable adherent surface film as a protective layer in the ceramic green laminates production to reduce and/or eliminate processing defects.
Still yet another purpose of the invention is to provide a novel thermally depolymerizable/decomposable adherent surface film as a protective layer in the ceramic green laminates production to reduce and/or eliminate processing defects caused during lamination, handling, and/or sizing/dicing operations.
Therefore, in one aspect this invention comprises a method of protecting an unsintered structure having at least one defect-free surface feature, comprising:
(a) placing at least a portion of at least one thermally depolymerizable/decomposable layer over said surface feature on said unsintered structure, wherein said thermally depolymerizable/decomposable layer has the characteristics of being thermally bondable to at least a portion of said unsintered structure and to at least a portion of said surface feature on said unsintered structure during lamination and being thermally decomposable without leaving any carbonaceous residue during subsequent sintering;
(b) applying pressure onto at least a portion of said thermally depolymerizable/decomposable layer, such that at least a portion of said thermally depolymerizable/decomposable layer conforms to at least a portion of the surface topography of said surface feature and said unsintered structure, and wherein at least a portion of said thermally depolymerizable/decomposable layer further adheres to at least a portion of the surface of said unsintered structure, and thereby protects said unsintered structure.
In another aspect this invention comprises an unsintered structure comprising at least one semiconductor substrate having at least one metallized feature and at least a portion of at least one thermally depolymerizable/decomposable layer conformably secured to a portion of said metallized feature and said at least one semiconductor substrate.